Field of the Invention
This invention is directed to a method and apparatus for generating an enhanced image for display from medical imaging data of a subject, in particular for elongated features of interest in an image volume.
Description of the Prior Art
The definition of regions or volumes of interest (ROI/VOI) is a typical precursor to quantitative analysis of medical images, such as nuclear medicine emission images (for example, PET or SPECT). Such regions may be defined around areas of high intensity which correspond to high tracer uptake (hotspots). For example, in FDG-PET images for oncology, such areas may be indicative of the presence of a tumor. Oncology physicians frequently annotate lesions in PET scans for the purpose of making a diagnosis, or for use in radiotherapy. The mean or maximum tracer uptake can aid a reader in determining the likelihood of cancer. In longitudinal studies, considering the change in intensity or uptake on corresponding VOIs from images at different temporal stages may be used to determine whether a tumor has regressed.
In oncology the identification, diagnosis, follow-up, and reporting of lesions are key steps in the clinical routine. Bone metastases (in the ribs and spine, for example) occur in many cancer types. The PET tracer F-18 sodium fluoride (18F—NaF), which features an increased uptake in osteolytic and osteoblastic bone lesions, can be used for imaging bone lesions. It has been shown that twice as many benign as well as malignant lesions will be visualized on 18F—NaF PET bone imaging versus conventional 99 mTc phosphonate SPECT or planar imaging. As a consequence, 18F—NaF PET results changed clinical management in about 18% of patients.
The detection and reporting of bone lesions can be cumbersome, particularly for patients with multiple lesions or wide-spread metastases. As a consequence, the manual detection and reporting of bone lesions is often time consuming and hence also prone to errors. In case of multiple lesions, e.g., at different locations along different ribs, the individual locations are frequently not properly documented due to time restrictions in clinical routine.
PET/SPECT bone scans are typically read on either a slice-by-slice basis (axial, coronal, sagittal) or by means of 3D MIPs. Each finding then needs to be manually reported (left/right rib, rib number, position along rib). However, after identification of a lesion along a particular rib, this information needs to be manually obtained by, e.g., counting the ribs visible in the 3D volume. As a consequence, detailed reporting of many lesions can be time-consuming and is often avoided for cases with multiple lesions. For follow-up examinations, the 3D volume data can be either visually compared or the different scans can be aligned to each other (e.g., using a registration algorithm). However, an automatic registration might be error-prone if the local morphology has significantly changed, e.g., due to therapy or disease progression. Moreover, quantitative comparison between different lesions is only possible if these lesions have actually been reported.
Using CT imaging only, WO 2006/050102 proposed a 2D visualization technique, in the following referred to as “rib unfolding”, which improves the detectability of rib lesions. To this end, the centerline of each rib is extracted. Then, for each rib a 2D projection of its centerline (often also referred to as “curved planar reformation” (CPR)) is visualized. Coupling this technique with rib labelling, lesions and corresponding rib information (left/right rib, rib number) can be identified and used for reporting.
An example of this technique is shown in FIG. 1, illustrating an example system using CT-based rib unfolding. In the top left frame (100), the unfolded ribs (102) are visualized in 2D incl. rib labels whereas the top right frame (104) shows a cross-sectional MPR to the currently selected rib (106) position. The traditional MPR views (axial, coronal, sagittal —108, 110, 112) are shown at the bottom.
However, using CT imaging only, rib lesions are often hard to detect as they may lack contrast to normal ribs and also may appear darker or brighter than healthy bone. As a consequence, each rib still requires carefully examination using the rib unfolded view in combination with traditional MPR images.